A photovoltaic system includes a solar cell string in which a plurality of solar cell modules are connected in series. Each solar cell module includes a plurality of solar cells which are connected in series, and a bypass diode that bypasses a current path of the solar cells is connected in parallel to each solar cell module.
The bypass diode of the solar cell module may be subject to a disconnection fault, and Patent Literatures 1 to 3 disclose techniques of detecting that a bypass diode has a disconnection fault.
Specifically, in the configuration described in Patent Literature 1, a current with a prescribed current value flows from a negative electrode of a solar cell string to a positive electrode thereof, a potential difference between the negative electrode and the positive electrode of the solar cell string is measured, and whether a bypass diode has malfunctioned is determined on the basis of the measured potential difference.
In the configuration described in Patent Literature 2, a reverse voltage with a prescribed value based on a negative electrode of a solar cell string is applied to a positive electrode thereof, a current value of a current flowing from the negative electrode of the solar cell string to the positive electrode is measured, and whether a bypass diode malfunctions is determined on the basis of the measured current value.
In the configuration described in Patent Literature 3, an AC power supply is controlled such that a bypass diode is biased forward in a solar cell panel body, and whether the bypass diode has a disconnection fault is determined on the basis of an input voltage or an input current and an output voltage or an output current at that time.
When a disconnection fault of a bypass diode is left as it is, there is no problem in a case in which a solar cell connected in parallel to the bypass diode with a disconnection fault generates electric power normally. However, when the solar cell malfunctions or when the solar cell is overshadowed, a current flows generally through the bypass diode but a current flows continuously through the solar cell which malfunctions or is overshadowed when the bypass diode has a disconnection fault. The solar cell which malfunctions or is overshadowed serves as a resistor and thus rises in temperature when a current flows therein, which is dangerous.